An electrical connector may include a plurality of leadframe assemblies disposed adjacent to one another in a connector housing. The connector may have a mounting interface that defines a first plane and mating interface that defines a second plane. Where the plane of the mating interface is orthogonal to the plane of the mounting interface, the connector may be referred to as a right-angle connector. Where the plane of the mating interface is parallel to the plane of the mounting interface, the connector may be referred to as a mezzanine connector.
Each such leadframe assembly may include a leadframe housing, which may be made of a dielectric material, such as a plastic, for example. A plurality of electrical contacts may extend through the leadframe housing. The contacts may be made of an electrically conductive material. The contacts may be stamped from a sheet of electrically-conductive material to form a leadframe. The leadframe housing may be overmolded onto the leadframe. Such a leadframe assembly may be referred to as an insert-molded leadframe assembly (IMLA).
Each contact may have a mating end, which may be a receptacle, blade, or other desirable mating end. Each contact may have a respective mounting end, which may be an eye-of-the-needle type mounting end, or a pin, ball, or other desirable mounting end, or terminate in a fusible mounting element, such as a solder ball, for example.
The mating ends of the contacts within a leadframe assembly may form a linear array extending along a first direction. The mating ends of the contacts may be arranged along a common centerline that extends along the first direction. The mounting ends of the contacts may form a linear array extending along a second direction, which may be parallel to the first direction (in the case of a mezzanine connector) or perpendicular to the first direction (in the case of a right angle connector). The mounting ends of the contacts may align along a common centerline that extends along the second direction.
Differential signal pairs of electrical contacts may be arranged edge to edge (i.e., edge-coupled) or broadside-to-broadside (i.e., broadside-coupled). Contacts may be arranged in a signal-signal-ground arrangement along either columns or rows.
A differential signal pair has a differential impedance between the positive conductor and negative conductor of the differential signal pair. Differential impedance is defined as the impedance existing between two signal conductors of the same differential signal pair, at a particular point along the length of the differential signal pair. It is desirable to control the differential impedance to match the impedance of the electrical device(s) to which the connector is connected. Matching the differential impedance to the impedance of electrical device minimizes signal reflection and/or system resonance that can limit overall system bandwidth. Furthermore, it is desirable to control the differential impedance such that it is substantially constant along the length of the differential signal pair, i.e., such that each differential signal pair has a substantially consistent differential impedance profile.
The differential impedance profile can be controlled by the positioning of the signal and ground contacts. Specifically, differential impedance may be determined by the proximity of the signal contact to an adjacent ground contact, and by the gap between edges of signal contacts within a differential signal pair.
To maintain acceptable differential impedance control for high bandwidth systems, it is desirable to control the gap between contacts to within a few thousandths of an inch. Gap variations beyond a few thousandths of an inch may cause an unacceptable variation in the impedance profile; however, the acceptable variation is dependent on the speed desired, the error rate acceptable, and other design factors.
In addition to conductor placement, differential impedance may be affected by the dielectric properties of material proximate to the conductors. Generally, it is desirable to have materials having very low dielectric constants adjacent and in contact with as much of the conductors as possible. The use of air rather than plastic as a dielectric provides a number of benefits.
Additional background may be found in U.S. Pat. No. 7,270,574, U.S. Pat. No. 6,994,569, and U.S. Patent Application Ser. No. 61/141,990, filed Dec. 31, 2008, the disclosure of each of which is incorporated herein by reference.